Upgrading from yoflash 4 to yoflash 5 should be pretty straight forward but please, please, PLEASE remeber to make a backup before you upgrade to yoflash 5.
When upgrading to yoflash 5; I have wirrten the installer that automatically converts the tags from yoflash to Joomla and also the categories from yoflash to Joomla. This worked mostly fine, however, if you have subcategories, I am afraid to have to make the subcategories again, because I coldn't really traverse the tree structure of the yoflash catagory system.
Also, your games will be converted to be compaible with yoflash 5. As I have written in the forums before, I don't support Flashgames anymore, however, they will be converted as well. But I am encouraging you, for your and your users safety, to delete flashgames. Actually, since yoflash 4 is so very old, I actually encourage you to delete all your games and start again; mostly to avoid duplicate entries and allow fullscreen support.
Yoflash tries to add an id for fullscreen support to your embed codes, however, this does not always work. If this is the cse, go to the game in question and edit the embed code by inserting a HTML-id called framegame.
That is:
id="framegame"
After the update process has finished please go to yoflash->options and go through them. Don't forget to save them.
You will also have to edit all yoflash menu items, as the category-ids have changed. Please also take a look at the "options"-tab and make sure that all settinsg are correct.
That should be it. If everything did happen correctly you should have succesfully upgraded to Yoflash 5.